Human anti-epidermal growth factor receptor single-chain antibodies

ABSTRACT

Human anti-epidermal growth factor receptor (EGFR) single-chain antibodies (scFvs) were isolated from a human IgM phage display library using purified epidermal growth factor receptor as antigen. Two isolates with different amino acid sequences were identified by ELISA as epidermal growth factor receptor-specific. The scFvs bind to the full length epidermal growth factor receptor and the truncated and/or mutated epidermal growth factor receptor on human cells. These anti-EGFR-scFvs are useful as therapeutic and/or diagnostic agents.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a division of U.S. patent application Ser.No. 09/976,118, filed Oct. 12, 2001, now U.S. Pat. No. 6,699,473, whichclaims benefit of patent application U.S. Ser. No. 60/240,353, filedOct. 13, 2000, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the fields of molecularbiology and monoclonal antibody technology. More specifically, thepresent invention relates to human single-chain antibodies that bindspecifically to the epidermal growth factor receptor.

2. Description of the Related Art

The epidermal growth factor receptor (EGFR) is a 170 kDa transmembraneglycoprotein consisting of an extracellular ligand binding domain, atransmembrane region and an intracellular domain with tyrosine kinaseactivity. The binding of growth factors, EGF or TGFα, to the epidermalgrowth factor receptor results in receptor dimerization,auto-phosphorylation and induction of a tyrosine kinase cascade, leadingultimately to DNA synthesis and cell division.

The epidermal growth factor receptor gene (c-erb-1), located onchromosome 7, is homologous to the avian erythroblastosis virus oncogene(v-erbB) that induces malignancies in chickens. The v-erbB gene encodesfor a truncated protein product that lacks the extracellular ligandbinding domain. The tyrosine kinase domain of the epidermal growthfactor receptor has been found to have 97% homology to the v-erbBtransforming protein.

The epidermal growth factor receptor is overexpressed in a number ofmalignant human tissues when compared to their normal tissuecounterparts. The gene for the receptor is both amplified andoverexpressed in a number of cancer cells. Overexpression of theepidermal growth factor receptor is often accompanied by theco-expression of the growth factors, EGF and TGFα, suggesting that anautocrine pathway for control of growth may play a major part in theprogression of tumors.

A high incidence of overexpression, amplification, deletion andstructural rearrangement of the gene coding for the epidermal growthfactor receptor has been found in biopsies of brain tumors. In fact, theamplification of the epidermal growth factor receptor gene inglioblastoma multiforme tumors is one of the most consistent geneticalterations known, with the EGFR being overexpressed in approximately40% of malignant gliomas. In addition to glioblastomas, abnormalepidermal—growth factor receptor expression has also been reported in anumber of squamous epidermoid cancers and breast cancers. Many patientswith tumors that overexpress the epidermal growth factor receptor have apoorer prognosis than those who do not. Consequently, therapeuticstrategies which can potentially inhibit or reduce the aberrantexpression of the EGFR are of great interest as potential anti-canceragents.

Since the advent of hybridoma technology to produce murine monoclonalantibodies (mAbs) developed by Milstein and Köhler in 1975 (1), thetherapeutic potential of antibodies is beginning to come to fruition forcancer therapy. There are many reports describing a few antibodies whichinhibit cell proliferation of epidermal growth factorreceptor-overexpressing cell lines (2–6). One such mouse antibody, mAb225, was shown to inhibit cell proliferation and block ligand-inducedepidermal growth factor receptor tyrosine kinase activity (2–3, 7).Further analysis showed mAb 225 induced a G₁ growth arrest and activatedan apoptotic pathway after a 24 h exposure to increasing concentrationsof antibody (8).

Other monoclonal antibodies which bind to the epidermal growth factorreceptor and block ligand binding also show promise for cancer therapy.One group of rat monoclonal antibodies showed a dramatic antitumoreffect in xenograft mouse models, with one antibody, ICR62 curing 4 outof 8 mice of the tumor (9). However, the problem with rat and mousemonoclonal antibodies or even the human-mouse chimeric antibody is thepossibility of an immune or allergic response with prolonged treatment(10–13).

In order to avoid the human anti-murine antibody (HAMA) response inhumans due to the repeated administration of murine mAbs, it ispreferable to use human antibody in therapy or diagnostics. A 100% humanmonoclonal antibody against the epidermal growth factor receptor,E7.6.3, has been shown to completely eradicate human tumor xenografts inmice (4). This antibody is expected to elicit a minimal immune responsein humans and shows promise for future cancer therapy. However due tothe heterologous vascular structure around the tumor and the molecularsize of the antibodies, monoclonal antibodies penetrate the tumor poorlyand are unevenly distributed around the tumor.

In order to improve on the use of monoclonal antibodies, intactmonoclonal antibodies have been reduced in size to antibody fragments orsingle-chain antibodies (scFvs). Therefore the development of humananti-EGFR scFvs will enhance its use as a diagnostic and/or therapeuticagent. One advantage of single-chain antibodies is their ability topenetrate deeper into the tumor (14). Thus, these molecules maypotentially be more efficacious than intact antibodies for systemicadministration. Also single-chain antibodies can be expressedintracellularly (intrabodies) and targeted to a subcellular compartmentof the tumor cell or be secreted by the tumor cell and bind in anautocrine/paracrine fashion.

The prior art is deficient in the lack of a 100% human single-chainantibody that binds to the epidermal growth factor receptor. The presentinvention fulfills this longstanding need and desire in the art.

SUMMARY OF THE INVENTION

The present invention provides a 100% human single-chain antibody (scFv)which binds to the epidermal growth factor receptor. Two single-chainantibodies were isolated from a human IgM phage display library usingpurified epidermal growth factor receptor as antigen, and identified byELISA as epidermal growth factor receptor-specific. Sequence analysisconfirmed the two isolates as individual clones based on differences intheir nucleotide and putative amino acid sequences. One single-chainantibody was shown to bind to the native full length epidermal growthfactor receptor and the truncated and/or mutated epidermal growth factorreceptor on human cells.

The present invention is directed to a human anti-epidermal growthfactor receptor single-chain antibody having a sequence of SEQ ID No. 1(clone 6) or SEQ ID No. 2 (clone 63), as well as DNA molecules andexpression vectors that encode for the expression of the claimed humananti-epidermal growth factor receptor single-chain antibody.

The present invention is also drawn to a pharmaceutical compositioncomprising the disclosed human anti-epidermal growth factor receptorscFv and a therapeutic and/or diagnostic agent. Preferably, thetherapeutic and/or diagnostic agent can be a toxin, a chemotherapeuticagent, a radioisotope, a transition metal or a gene therapy vector.

The present invention is also drawn to a method of treating or imaging atumor, comprising the step of administering to a patient in need of suchtreatment or detection an effective amount of a radiolabeled anti-EGFRsingle-chain Fv of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the matter in which the above-recited features, advantages andobjects of the invention, as well as others which will become clear, areattained and can be understood in detail, more particular descriptionsof the invention briefly summarized above may be had by reference tocertain embodiments thereof which are illustrated in the appendeddrawings. These drawings form a part of the specification. It is to benoted, however, that the appended drawings illustrate preferredembodiments of the invention and therefore are not to be consideredlimiting in their scope.

FIG. 1 shows the phagemid, pSEX81, which is optimized for surfaceexpression on the M13 bacteriophage. Depicted here is a single-chainantibody cloned into the multiple cloning site, in-frame with the pelBleader sequence and gene III M13 protein.

FIG. 2 shows the putative amino acid sequences of anti-EGFR scFv clonespSEX81-6 and pSEX81-63. Clones were sequenced both directions usingprimers from the pelB leader sequence, the gene III protein and twocomplementary primers annealing to the alpha tubulin linker sequence.The heavy chain variable region (V_(H)) and light-chain variable region(V_(L)) are identified with their respective CDRs (bold) as described(16). *identifies identical amino acids.

FIG. 3 shows the eukaryotic secreting plasmid, pSECTAG/Bpu/neo which wasmodified from pSECTAG/Friendly (Invitrogen). The neomycin gene replacedthe zeomycin gene and a Bpu 1102I restriction enzyme site was addedin-frame with the Ig leader sequence.

FIG. 4 shows the analysis of secretory anti-EGFR-scFv from U87MG celllines stably transfected with vector (pSECTAG) or anti-EGFR scFv clone 6(p6.34). FIG. 4A shows immunoprecipitation of scFv from cell lysates ofpSECTAG (lane 1) and p6.34 (lane 2) using anti-myc antibody. FIG. 4Bshows immunoprecipitation of secretory scFv from culture medium ofpSECTAG (lane 1) and p6.34 (lane 2) using anti-alpha tubulin antibody.Anti-myc antibody was used to detect scFv for both immunoblots in FIGS.4A and 4B. FIG. 4C shows ELISA using cell culture medium, or culturemedium from pSECTAG, p6.34 or anti-EGFR mAb (Sigma) to detect binding tothe epidermal growth factor receptor antigen. ScFvs were detected usinganti-myc-HRP antibody and anti-epidermal growth factor receptor mAb wasdetected with anti-mouse IgG-HRP antibody and developed with OPD(Sigma).

FIG. 5 shows FACS analysis for the detection of anti-epidermal growthfactor receptor scFv bound to the extracellular domain of the epidermalgrowth factor receptor. The cells, U87MG, U87MG.wtEGFR and U87MG.ΔEGFRwere incubated with culture medium, culture medium from pSECTAG or p6.34for 30 min at 4° C. The cells were washed, then incubated with ratanti-alpha tubulin followed by FITC-labeled anti-rat antibody.

Other and further aspects, features, and advantages of the presentinvention will be apparent from the following description of thepresently preferred embodiments of the invention given for the purposeof disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Because the administration of murine monoclonal antibodies to humansresulted in human anti-murine antibody (HAMA) response, hindering anytherapeutic and/or diagnostic potential, the monoclonal antibodies hadto be modified. Genetic engineering techniques were used to develophuman-murine chimeric monoclonal antibodies. An alternative solution wasto develop single-chain antibodies (scFvs). Initially murine scFv wereisolated and now technology has progressed to screening naive humanphage display libraries for therapeutically and/or diagnostically usefulsingle-chain antibodies of human origin (30–32).

Over the past 10 years, a variety of mouse and human single-chainantibodies have been isolated, including mouse scFvs which bind to thecell surface receptors, epidermal growth factor receptor and erbB-2 (23,27, 33). Cell proliferation was inhibited when EGFR-overexpressing celllines were transfected with a plasmid encoding murine anti-EGFR scFvstargeted to the endoplasmic reticulum (ER) or secretory pathway (23,27). Inhibition of cell proliferation was obtained whenerbB-2-overexpressing cell lines were transfected with a plasmidresulting in the production of murine single-chain antibodies whichbinds the erbB-2 receptor in the ERbut no inhibition of cellproliferation was detected with a cytoplasm-targeted scFv (33). Eventhough both of the single-chain antibodies bound to the extracellulardomain of their respective receptor they were expressed as anintracellular scFv (intrabody). The intrabodies were directed to thelumen of the ER to bind the receptor as it was being processed forglycosylation, thereby decreasing the amount of receptor expressed onthe plasma membrane and inhibiting cell proliferation. To obtain thegreatest anti-proliferative effect, the optimal expression and targetingof anti-EGFR single-chain antibodies to the subcellular componentsinvolved in epidermal growth factor receptor expression should beundertaken.

The ability of a single-chain antibody to inhibit tumor cellproliferation has considerable potential for cancer gene therapy on itsown merit. Moreover, the ability of a scFv to sensitize tumor cells toradiation or chemotherapy treatments will enhance their therapeuticpotential. Tumor cells either transfected with scFv expressing plasmidDNA or transduced with viral vectors have shown an increased sensitivityto radiation and/or chemotherapy drugs in vitro and in vivo (34, 35).The anti-erbB-2 scFv, pGT21, was shown to sensitize ovarian cancercells, SKOV3, to cis-DDP (34). The increased sensitization to cis-DDPwas shown to be related to the down-modulation of the erbB-2 protein bytargeting the scFv to the ER. The same scFv also sensitized tumor cellsto radiation in vitro and in vivo (35). However, a major limitation forthese scFvs is the fact that the majority are murine and thereforepotentially immunogenic in human.

The present invention discloses a 100% human single-chain antibody(scFv) which binds to the epidermal growth factor receptor. Two scFvswere isolated from a human IgM phage display library using purifiedepidermal growth factor receptor as antigen, and identified by ELISA asepidermal growth factor receptor-specific. Sequence analysis confirmedthe two isolates as individual clones based on differences in theirnucleotide and putative amino acid sequences. One scFv was shown to bindto the native full length epidermal growth factor receptor and thetruncated and/or mutated epidermal growth factor receptor on humancells.

As used herein, the term “monoclonal antibody” means an antibodycomposition recognizing a discrete antigen determinant. It is notintended to be limited with regard to the source of the antibody or themanner in which it is made.

As used herein, single chain antibodies or scFvs are polypeptides whichconsist of the variable (V) region of an antibody heavy chain linked tothe V region of an antibody light chain with or without aninterconnecting linker. This comprises the entire antigen binding site,and is the minimal antigen binding site. These single-chain antibodiesmay be produced in bacteria, yeast or eukaryotic cells.

An “antigen-binding site” refers to the part of an immunoglobulinmolecule that participates in antigen binding. The antigen binding siteis formed by amino acid residues of the N-terminal variable regions ofthe heavy and light chains. Three highly divergent stretches within theV regions of the heavy and light chains are referred to as“hypervariable regions” which are interposed between more conservedflanking stretches known as “framework regions” or “FRs”. In an antibodymolecule, the three hypervariable regions of a light chain and the threehypervariable regions of a heavy chain are disposed relative to eachother in three dimensional space to form an antigen binding “surface”.This surface mediates recognition and binding of the target antigen. Thethree hypervariable regions of each of the heavy and light chains arereferred to as “complementarity determining regions” or “CDRs” and arecharacterized, for example by Kabat et al., Sequences of proteins ofimmunological interest, 4th ed., U.S. Dept. Health and Human Services,Public Health Services, Bethesda, Md. (1987).

As an agent by itself, the scFv disclosed herein may inhibit and/orblock the growth of epidermal growth factor receptor-expressing humancells. The human anti-epidermal growth factor receptor scFv may alsoinduce apoptosis and cell death in human cells that express epidermalgrowth factor receptor. A toxin, chemotherapeutic agent, a transitionmetal or radioisotope generally known in the art can be covalently ornon-convalently conjugated to the scFv of the present invention, whichwould then target the agent to epidermal growth factorreceptor-expressing human cells. The scFv disclosed herein may also beused as a part of a bi-specific scFv or some other combination witheither itself or another scFv. Furthermore, all or portions of the scFvdisclosed herein may be used to target viral or bacterial gene therapyvectors or other agents to bind to epidermal growth factorreceptor-expressing human cells. The portions of the scFv could be assmall as one complementarity determining region (CDR) or a combinationof CDRs from one or both variable regions.

One object of the present invention is to target a scFv to a particularcellular process as a powerful therapeutic technique. Combining thetargeted scFv with a gene-based therapeutic approach may enhance theefficacy of single-chain antibodies. The realization of the goals of thecurrent invention will allow for the design of cancer gene therapytreatment using intratumoral injection of a viral vector for successfultransduction of a therapeutic scFv to be used in combination withradiation and/or chemotherapy drugs.

A number of methods can be used to deliver the single-chain antibodiesof the present invention to tumor cells. In the ex vivo method, the scFvis expressed in bacterial cells (14, 36–37) or eukaryotic cells (24),then isolated and purified prior to administration to the tumor celllines or tumors implanted in mice. The purified scFv may be administereddirectly or labeled with a radioisotope, transition metal or toxin priorto administration (38–41). Also, the single-chain antibodies can beengineered to express a bacterial toxin protein on the C-terminal end toenhance the therapeutic potential of the scFv (37). The administrationof an ex vivo produced scFv will rapidly localize and penetrate thetumor before being quickly cleared from the circulatory system (14,38–39).

The in vivo expression of single-chain antibodies can result fromtransiently or stably transfecting cells with DNA (24–25) or transducingcells with viral vectors. DNA transfer can be accomplished by a varietyof standard techniques, such as calcium phosphate, DEAE dextran,electroporation or lipophilic reagents or by using a viral vector totransport the DNA into the cells. Most DNA transfection methods workvery well for in vitro experiments; however, viral vectors may be moreadvantageous for in vivo protocols. Viral vectors commonly used for genetherapy include retrovirus, adenovirus, adeno-associated virus andherpesvirus.

The invention also includes biologically functional fragments of thesingle-chain antibodies described in this specification. Biologicallyfunctional fragments are those fragments sufficient for binding of theantibody fragment to epidermal growth factor receptor. Functionalfragments include polypeptides with amino acid sequences substantiallythe same as the amino acid sequence of the variable or hypervariableregions of the antibodies of the present invention. “Substantially thesame” amino acid sequence is defined herein as a sequence with at least70% percent homology to an amino acid sequence of an antibody of thepresent invention.

Furthermore, other “substantially homologous” modified antibodypolypeptides can be readily designed and manufactured utilizing variousrecombinant DNA techniques known to those skilled in the art.Modification of the genes may be readily accomplished by a variety ofwell-known techniques such as site-directed or random mutagenesis. Thesemodifications can include amino acid additions, deletions,substitutions, preferably conservative, and other changes in thesequence of the polypeptide while retaining the appropriate property orbiological activity.

Alternatively, polypeptide fragments comprising only a portion of theprimary antibody structure and possessing binding and/or effectoractivities may be produced. Also because, like many genes, theimmunoglobulin-related genes contain separate functional regions, eachhaving one or more distinct biological activities, the genes may befused to functional regions from other genes to produce fusion proteins(e.g. immunotoxins) having novel properties or novel combinations ofproperties.

The current invention is directed to a human anti-epidermal growthfactor receptor single-chain antibody having a sequence of SEQ ID No. 1(clone 6) or SEQ ID. No. 2 (clone 63), as well as DNA molecules andexpression vectors that encode for the expression of the claimed humananti-epidermal growth factor receptor scFv.

The present invention is also drawn to a pharmaceutical compositioncomprising the disclosed human anti-epidermal growth factor receptorscFv and a therapeutic or diagnositic agent. Preferably, the therapeuticor diagnositic agent can be a toxin, a chemotherapeutic agent, atransition metal, a radioisotope or a gene therapy vector.

The following examples are given for the purpose of illustrating variousembodiments of the invention and are not meant to limit the presentinvention in any fashion.

EXAMPLE 1

Isolating EGFR-Specific Human Single-Chain Antibody (scFv)

In the screening of the phage library for anti-epidermal growth factorreceptor scFv, an IgM scFv display library with a calculated complexityof 2×10⁷ independent clones was constructed in pSEX81 (FIG. 1) asdescribed (15) using peripheral leukocyte cDNA prepared from healthydonors. The IgM phage display library was screened for expression ofscFvs which specifically bind the EGF receptor (EGFR). The phage librarywas suspended in 500 ml 2xYT-GA medium (17 g Tryptone, 10 g yeastextract, 100 mM glucose, 100 μg/ml ampicillin and H₂O to 1 liter) to aninitial OD₆₀₀ of 0.025. The cells were grown with shaking (240 rpm) at37° C. until an OD₆₀₀ of 0.1 at which point the cells were superinfectedwith helper phage, M13K07 (Amersham Pharmacia Biotech), at an MOI of 20.After the addition of helper phage, the cells were mixed gently and leftundisturbed for 15 min at 37° C. followed by shaking (240 rpm) for 45min. The medium was replaced by separating the bacteria at 1500×g for 10min at room temperature (RT), then the bacterial pellet was suspended in500 ml 2xYT-AK medium (17 g Tryptone, 10 g yeast extract, 50 μg/mlkanamycin, 100 μg/ml ampicillin and H₂O to 1 liter). The culture wasincubated at 37° C. with shaking (240 rpm) for 7 h. The cells wereseparated from the medium by centrifugation at 6500×g for 15 min at 4°C. The bacteriophage was precipitated out of the supernatant by adding ⅕volume PEG/NaCl solution (200 g PEG-600, 146.1 g NaCl, up to 1 literwith H₂O) and incubating the medium overnight at 4° C.

During the PEG precipitation, affinity purified EGFR (Sigma) in 100 mMsodium carbonate, pH 9.6 was adsorbed to a MaxiSorb Immunotube (Nunc,Rochester, N.Y.) at a concentration of 5–10 μg/ml for 18 h at 4° C. Thenext day, the immunotube was washed 3 times with PBS, then blocked with2% skim milk in PBS-T (PBS with 0.05% Tween-20) for 2–3 h at roomtemperature (the immunotubes were blocked with 0.5% casein-PBS for thesecond round and 2% skim milk-PBS for the third round). The immunotubewas washed 3 times with PBS-T, then stored at 4° C. until ready to use.

The PEG precipitated bacteriophage was separated from the supernatant byhigh speed centrifugation (10,000×g for 20 min at 4° C.). The pellet wassuspended in 4 ml ice-cold phage dilution buffer (10 mM Tris-HCl, pH7.5, 20 mM NaCl, 2 mM EDTA). The bacteriophage lysate was clarified at12,000×g for 5 min at 4° C. The supernatant was collected and stored at4° C. until the colony forming units (cfu) titer was determined.

To determine the cfu titer, an aliquot of the PEG-concentratedbacteriophage was diluted 10-fold up to 10⁻¹⁰ dilution, then 10 μl ofthe 10⁻⁷ to 10⁻¹⁰ dilutions was added to 90 μl of an exponentiallygrowing XL1-Blue culture in LB-tet broth (10 g tryptone, 5 g yeastextract, 0.5 g NaCl, 15 μg/ml tetracycline in 1 liter H₂O). The viruswas allowed to adsorb for 20–30 min at RT, then mixed with 3 ml ofLB-amp (LB broth with 100 μg/ml ampicillin) soft agar (0.5% agar) cooledto 45° C., and immediately overlaid upon an LB-amp agar plate. Theplates were inverted and incubated overnight at 37° C. The titer wasdetermined by the number of ampicillin-resistant colonies that haveformed at each dilution.

EGFR-specific scFvs were recovered from the phage library by absorbingloll to 10¹² cfu in 4 ml PBS-T to the EGFR-coated immunotubes withrocking for 2 hours at RT. The immunotubes were washed 20 times withPBS-T followed by 20 times with PBS. The EGFR-specific virus was elutedin 1 ml 100 mM triethylamine (Sigma) for 5 min at room temperature, thenimmediately neutralized with 1 ml 1 M Tris-HCl, pH 7.4 and stored on iceuntil ready to infect XL1-Blue cells.

To amplify the EGFR-specific scFv bacteriophage, XL1-Blue cells weregrown in 20 ml LB-tet broth until an OD₆₀₀ of 0.4. Theneutralized-eluted phage was added to the culture, allowed to adsorbundisturbed for 15 min at 37° C., followed by shaking (240 rpm) for 45min. An aliquot was remove (200 μl) to determine the cfu titer, bymaking 10-fold dilutions of the 200 μl aliquot in SOB-GA broth (up to10⁻⁴), then 100 μl from each dilution was spread onto an SOB-GA agarplate (100 mm²) and incubated overnight at 37° C. The cfu titer wasdetermined by counting the number of ampicillin resistant colonies. Theremaining cells were separated from the broth by centrifugation at2000×g for 5 min at RT. The cell pellet was suspended in 1000 μl SOB-GAmedium (20 g tryptone, 5 g yeast extract, 0.5 g NaCl, 50 mM MgSO₄, 100mM glucose, 100 μg/ml ampicillin), then spread onto 3 SOB-GA agar plates(150 mm²). After the plates dried, they were inverted and incubated at37° C. for 18–24 h. The colonies grown on the 150 mm² plates wereremoved by scraping the bacteria into 10 ml SOB-GA broth per plate. Thebacteria were pooled, then used to inoculate a 250 ml 2xYT-GA brothculture to an OD₆₀₀ of 0.025. Glycerol was added to a concentration of20% to the remaining bacteria and stored at −80° C. To increase thespecificity, the process for isolating EGFR-specific scFvs was repeated2 additional times.

Putative anti-EGFR-specific scFv clones were isolated from the 2nd roundand 3rd round of screening. All clones were stored at −80° C. as a 20%glycerol stock of an overnight broth culture grown in 2xYT-GA broth.

Small Scale Phage Rescue

The scFv bacterial clones were used to inoculate 0.2 ml 2xYT-GA mediumand grown overnight at 37° C. Ten μl of the overnight culture wastransferred to 1 ml 2xYT-GA medium and incubated with shaking (300 rpm)at 37° C. for 3 hours. M13K07 helper phage (10¹⁰ cfu) was added to eachculture, mixed gently and set undisturbed for 15 min at 37° C., thenshaked for 45 min at 300 rpm. The cells were separated by centrifugationat 1000×g for 5 min at room temperature and the supernatant removed,then 1 ml 2xYT-AK medium was added to the cell pellet and incubated withshaking for 7 hours. The cells were removed by centrifugation and thesupernatant collected. The supernatant was stored at 4° C. for up to 3days.

Screening Clones by Phage ELISA

The 96-well MaxiSorb immunoplates (Nunc, Rochester, N.Y.) were coatedwith 1 μg/ml affinity purified EGFR antigen (Sigma) in 100 mM sodiumcarbonate, pH 9.6 buffer. The antigen was allowed to adsorb overnight at4° C., then the antigen was removed and the wells were washed 3 timeswith PBS-T. The wells were blocked with 2% skim milk-PBS for 2 hours atroom temperature. The wells were washed 3 times with PBS-T, then 100 μlof rescued phage was added per well and incubated at room temperaturefor 2 hours. The wells were washed 3 times with PBS-T, then 100 μl of a1/1000 dilution of anti-M13-HRP (Stratagene, LaJolla, Calif.) was addedto each well and incubated for 1 h at room temperature. The wells werewashed 5 times with PBS-T, then 200 μl of the TMB enzyme substrate(Sigma) was added per well. The ELISA plates were incubated at roomtemperature for 30 minutes, then read at 650 nM. Wells equal to andabove OD₆₅₀=0.1 were considered positive and below OD₆₅₀=0.1 wereconsidered negative.

EXAMPLE 2

Sequencing and Analysis of scFv Clones

After 3 rounds of phage panning, individual clones were identified byELISA as described above. Plasmid DNA was isolated and sequencedaccording to standard manufacturer's protocol for the ABI DNA sequencer(UAB Automated DNA Sequencing Core Facility). Plasmid DNA was sequencedboth directions initially using pelB and gene III primers. Internalsequencing primers were determined from the initial sequence data andsynthesized by Operon (Alameda, Calif.). After completion of the scFvsequence, the data was analyzed using SeqWeb software (Genetics ComputerGroup, Madison, Wis.) for alignment of complementary-determining regions(CDRs) with known variable-chain sequence data.

Two clones, pSEX81-6 and pSEX81-63, have been sequenced and theirputative amino acid sequences are shown in FIG. 2. The clones are in theorder, variable heavy chain (V_(H))-linker-variable light chain (V_(L)),with both clones containing a lambda V_(L) chain.

When comparing the two clones, there is a 48% amino acid identity in theV_(H) chain and an 87% amino acid identity in the V_(L) chain. Thehypervariable or complementarity-determining regions (as defined in ref.16) are located at the tips of the Fabs in a 3-dimensional structure andhave been shown to be primarily involved with antigen binding (17). TheCDR1-L region is 100% identical between the two clones, whereas theother CDRs vary from 2 amino acid differences in CDR3-L, CDR2-L andCDR1-H to 10 and 12 amino acid differences in CDR3-H and CDR2-H,respectively. With the high variability between the CDRs of these twoclones, each clone may bind to a different antigenic site on the EGFR.

EXAMPLE 3

Targeting the scFv to a Cellular Compartment and Expression of SecretoryscFv

In eukaryotic cells, scFvs can be targeted to specific subcellularcompartments by engineering the nucleotide sequence to express a proteinwith the appropriate signal sequences. In this way the scFvs can bemodified to be directed to a subcellular compartment where the antibodymight prove to be most effective. Recently, Lotti et al. showed that theC-terminal sequence KKXX from the adenovirus E19 protein would enhancethe localization of the protein to the cis-golgi complex with someretention in the ER (18). To direct the scFv to the cytoplasm, thehydrophobic amino acid core of the immunoglobulin secretory signalsequence was removed (19). The addition of a nuclear localization signalfrom the large T-antigen of SV40 virus, PKKKRKV (SEQ ID No. 3), to theN-terminal end can target the scFv to the nucleus (20).

To target mitochondria, the N-terminal presequence of the subunit VIIIof human cytochrome c oxidase was added to the N-terminal end of thescFv (21). Other investigators have directed scFvs to the lumen of theendoplasmic reticulum by including the endoplasmic reticulum retentionsignal (SEKDEL, SEQ ID No. 4) at the C-terminus of the polypeptide(22–25) scFvs can also be directed to the secretory pathway by theaddition of an immunoglobulin signal peptide on the N-terminal end(23–27).

In order to express the secretory scFvs in eukaryotic cells, the insertencoding the scFvs must be cloned downstream of an Igκ secretory leadersequence in a eukaryotic expression vector. To this end, the eukaryoticexpression vector, pSecTag (Invitrogen) was modified at the multiplecloning site to accept the restriction enzyme sites (Bpu1102I and NotI),in the correct orientation and in the proper reading frame between theleader sequence and the myc (mAB 9E10 epitope) and (His)₆ tags. Also,the eukaryotic antibiotic resistance gene was changed from zeomycin toneomycin, thus the plasmid is named pSecTag/Bpu/neo (FIG. 3).

Standard cloning techniques were employed to clone the scFv intopSecTag/Bpu/neo. Briefly, 20 ml LB-amp medium were inoculated withXL1-Blue cells expressing the pSEX81-scFv. After an overnight incubationat 37° C., the bacteria were recovered by centrifugation at 4000×g for 5min. The plasmid DNA were isolated using a Wizard DNA Purification kit(Promega, Madison, Wis.). The pSEX81-scFv plasmid DNA were digested withthe restriction enzymes, Bpu1101I and NotI, and separated by agarose gelelectrophoresis. The scFv fragment were recovered from the agarose gelusing AgarACE Enzyme (Promega). T4 DNA ligase were used to ligate thescFv fragment into the pSecTag/Bpu/neo plasmid which was digested withBpu1101I and NotI and agarose gel purified. The ligated DNA was use totransform E. coli Top 10F′ competent cells (Invitrogen) and plated ontoLB-A (LB medium with 100 μg/ml ampicillin) agar plates. After anovernight incubation at 37° C., individual colonies were selected andused to inoculate 5 ml LB-A broth cultures. Plasmid DNA was recoveredusing the Wizard DNA Purification kit and analyzed forpSecTag/Bpu/neo-scFv by PCR, amplifying the scFv clone between a T7promoter primer and a myc tag primer. No insert produced a 248 bp PCRproduct and a positive clone produced a PCR product between 800–1200 bp.

The positive clones were amplified in their bacterial host and theplasmid DNA was recovered using the Wizard PureFection Plasmid DNAPurification System (Promega). The low EGFR expressing human glioma cellline U87MG was transiently transfected with insert positive plasmid DNAor vector alone using the Lipofectin Reagent (Life Technologies).Forty-eight hours after transfection, culture medium was collected andanalyzed for secretory scFv to EGFR Stable transfects were isolated byselecting for antibiotic G-418 resistance with the scFv clones(U87MG-scFv) and vector clones (U87MG-pSecTag/Bpu/neo). The stabletransfects were subcultured in 96-well plates at a density, of less than1 cell per well. The culture medium from the confluent wells werescreened by ELISA testing for secreted anti-EGFR-scFv. The positivesubclones were subcultured in 96-well plates at a density of less than 1cell per well and the wells grown to confluent monolayers were screenedfor secreting anti-EGFR-scFv by ELISA. The positive subclones wereexpanded for further analysis.

EXAMPLE 4

Screening for Anti-EGFR-scFv by Immunoblot and ELISA

One of the stably transfected human glioma sublines, U87MG.6.34.A8(referred to as clone p6.34) was tested for its ability to secrete afunctional, anti-EGFR scFv. The anti-EGFR-scFvs were immunoprecipitatedfrom cell lysates and culture medium. Briefly, the cells were placed onice, washed three times with ice-cold PBS, lysed in ice-cold lysisbuffer (containing 0.025 M Tris-HCl, pH 7.5; 0.25 M NaCl, 0.005 M EDTA,1% v/v NP-40, 0.001 M phenylmethylsulfonylfluoride, 15 μg/ml aprotinin,10 μg/ml leupeptin, 0.001 M Na-orthovanadate, 0.05 M Na-fluoride and0.03 M Na-pyrophosphate) then clarified by centrifugation at 15,000×gfor 20 min at 4° C. Protein concentrations were determined using a BCAprotein assay kit (Pierce). Equal amounts of protein wereimmunoprecipitated with mouse anti-myc antibody (9E10 epitope,Stratagene) using Protein A/G beads (Pierce). For immunoprecipitation ofsecretory scFvs from the culture medium, four-day-old cell culturesupernatants were collected from the stably transfected cells. Equalvolumes (1 ml) were immunoprecipitated with rat anti-tubulin antibody(Serotec Inc., Raleigh, N.C.) using Protein A/G beads.

Screening for the expression and secretion of the scFvs was byimmunoblot, whereby the immunoprecipitated proteins were denatured byboiling in sample buffer (0.125 M Tris-HCl, pH 6.8; 10% glycerol, 1%SDS, 0.7 M β-mercaptoethanol and 0.25% bromophenol blue) for 3 min andseparated by SDS-PAGE then transferred to Immobilon-P membrane(Millipore Corp., Bedford, Mass.). Immunoblots were blocked in 10%milk-TBS-T (Tris-buffered saline with 0.05% Tween-20) for 1 hour at roomtemperature. Primary antibody, mouse anti-myc (Stratagene) was incubatedin 2% milk-TBS-T overnight at 4° C. Blots were washed three times inTBS-T followed by incubation with HRP (horseradish peroxidase) labeledsecondary antibody, anti-mouse Ig-horseradish peroxidase antibody(Sigma) at room temperature for 1 hour. The blots were washed threetimes with TBS-T and once with TBS. The blots were developed bychemiluminescence (Amersham Pharmacia Biotech, Piscataway, N.J.).

Results show that scFv was immunoprecipitated from the cell lysate (FIG.4A) and the culture medium. (FIG. 4B) of clone p6.34 but not from thecontrol cell line pSECTAG that was stably transfected with the parentvector pSECTAG/Bpu/Neo. These data indicated that scFv was translatedand processed into the secretory pathway. However, these data did notindicate whether clone p6.34 scFv binds to the EGFR antigen.

Therefore, culture medium from stably transfected cells was tested in anELISA for the expression of secretory scFv against EGFR. The culturemedium was clarified by low speed centrifugation (1000×g for 5 min at 4°C.) to remove any cells, then clarified at high speed centrifugation(10,000×g for 15 min at 4° C.) to remove any debris. Cell culture medium(100 μl) was added to each well and incubated for 2 h at 37° C. in a CO₂incubator. The wells were washed with PBS-Tween-20 (PBS-T). Secondaryantibody, anti-myc (mAb 9E10, Invitrogen) at a 1:1000 dilution in PBS-Twas added to each well and incubated for 1 hour at 22° C. After washingthe wells, a tertiary antibody, anti-mouse-HRP (Sigma) at 1:2000dilution in PBS-T was added to each well, then incubated for 1 h at 22°C. The wells were washed and developed with o-phenylenediamine (OPD,Sigma) and read at 450 nm. The results shown in FIG. 4C indicate thatclone p6.34 secretes scFv that binds to the purified EGFR antigen.

EXAMPLE 5

Binding of Anti-EGFR-scFv to the Extracellular Domain of EGFR

The ELISA data shown above indicates that clone p6.34 scFv binds todenatured EGFR, however it does not provide any information as to whichpart of the receptor was recognized by the scFv. The EGFR has threemajor domains, intracellular, transmembrane and extracellular, any ofwhich may serve as the binding site for clone p6.34. To examine whetherthe scFv binds to the extracellular portion of the receptor, a FACSanalysis was used for this determination. For this assay, culture mediumcollected from U87MG.pSECTAG or U87MG.pSECTAG.6.34.A8 was allowed tointeract with the cell surface of 3 different human glioma sublines;U87MG, U87MG.wtEGFR and U87MG.ΔEGFR (provided by Dr. H-J. Su Huang,UCSD).

The U87MG is the parent cell line into which the scFv clones were stablytransfected as well as stably transfected with wild-type EGFR(U87MG.wtEGFR) or the truncated EGFR, EGFRvIII (U87MG.ΔEGFR) (28–29).U87MG has a very low number of EGFR, which is one reason why cellproliferation of the stably transfected cell line, clone p6.34, does notappear to be affected by the anti-EGFR scFv (data not shown). TheU87MG.wtEGFR subline overexpresses a large number of EGFR/cell(estimated at >3×10⁶). The U87MG.ΔEGFR expresses the 135 kdal truncatedEGFR which is constitutively phosphorylated (29).

The FACS results shown in FIG. 5 indicates that the secretory scFv p6.34binds to the extracellular domain of U87MG.wtEGFR and U87MG.ΔEGFR. Theparent cell line, U87MG, does not have a significant number of receptorson its cell surface which results in no detectable scFv p6.34 binding.The data indicates that clone p6.34 produced a secretory scFv whichbound to the cell surface of cells which overexpress EGFR and truncatedEGFR (EGFRvIII). Since clone p6.34 bound to a common antigenic site onboth prominent forms of cancer-related EGFRs, this scFv might block thesurface expression of each receptor when presented in the propersubcellular compartment.

EXAMPLE 6

Radiolabelled Anti-EGFR-scFv for Early Detection of Breast Cancer

Many tumor-specific antigens have been identified as targets for imagingbreast cancer. HER-2/neu is overexpressed on 25%–30% of breast cancercells. The epidermal growth factor receptor, a receptor in the samefamily as HER-2/neu, has been found to be overexpressed in a highpercentage of human carcinomas. A compilation of the literatureestimates that approximately 30%–35% of the breast carcinomas haveincreased levels of epidermal growth factor receptor protein and theincrease of epidermal growth factor receptor expression correlates withthe loss of estrogen receptor and a poor prognosis.

With the increasing data on the relationship between the overexpressionof the epidermal growth factor receptor and poor prognosis, thisreceptor has become a target for breast cancer imaging. Radiolabelledmonoclonal antibodies (mAbs) have been used for imaging epidermal growthfactor receptor-overexpressing breast tumors. However, due to theheterologous vascular structure around the tumor and the molecular sizeof the antibodies, the monoclonal antibodies penetrate the tumor poorlyand are unevenly distributed around the tumor making imaging moredifficult.

In order to improve tumor imaging, intact monoclonal antibodies havebeen reduced to antibody fragments or single-chain antibodies. The shortplasma half-life for the scFv becomes an advantage for tumor imagingbecause tumor-to-blood ratios are higher than intact monoclonalantibodies and the rapidly eliminated scFv does not accumulate inextravascular spaces and non-target organs. Isotopes used for imagingtumors include ¹¹¹In, ⁶⁴Cu, ¹³¹I, ⁹⁹Y, and ^(99m)Tc. Technetium-99m isused in the following protocol because the techniques are available forboth direct and indirect scFv labelling and ^(99m)Tc is a low cost,readily available isotope with purely photon radiation, which is widelyused in clinical imaging. The 6 h half-life of ^(99m)Tc is an excellentcomplement to the scFv which has a rapid clearance from the circulationsystem allowing for high-contrast imaging.

The radiolabelled scFv of the present invention will be tested for anyloss of ability to bind to the epidermal growth factor receptor due tothe radiolabelling process. Then, the radiolabelled scFv can be use inmouse xenograft models to determine its ability to bind to large orsmall xenografts of high, moderate or low epidermal growth factorreceptor overexpressing breast cancer cells detected by a gamma camerawith computer-enhanced imaging.

Although tissue biodistribution is currently a standard method to assesspharmacokinetics in mice, it suffers from several drawbacks. First, theconcentrations of the radiolabelled peptides at each time point aremeasured from different mice and data are pooled for each separatelyevaluated group. Second, the number of time points to be sampled areoften limited to 3–5 points, consequently, the fast phase of tissueuptake is ignored. Because of the small size of the anti-epidermalgrowth factor receptor-scFv, the uptake and clearance are expected to befast in this study. Thus, the pharmacokinetics of the ^(99m)Tc-scFv willbe determined by dynamic imaging using a pinhole gamma camera, and theresults are useful for the development of non-invasive imaging methodfor early detection of breast cancer.

Breast Cancer Cell Lines

The following cell lines are purchased from ATCC (Manassas, Va.):MDA-MB-468, MDA-MB-231 and MCF-7. These cell lines are reported tooverexpress EGFR at levels ranging from low (10,000 receptors/cell,MCF-7), medium (100,000 receptors/cell, MDA-MB-231) and high (1,000,000receptors/cell, MDA-MB-468).

Radiolabelling of the anti-EGFR scFv

The indirect radiolabelling procedure, with the trihydroxamatbifunctional chelating agent trisuccin (42), is used for ^(99m)Tclabelling of the scFv. The protocol is in two steps consisting ofconjugation of trisuccin to the scFv (43), followed by theradiolabelling of the conjugate.

For trisuccin conjugation, the 50 μl solution of the scFv in DPBS isadded to 250 μL of a 50 mM PBS buffer at pH 8.1. The resulting solutionis stirred at 0° C. and the solution of OHA-NHS (5.7 g, 23.5 nmol) in 50μl of DMF is added. After 90 min at 0° C., the reaction is quenched byaddition of 20 μl of 2 M glycine in the PBS buffer and the reactionmixture is purified by dialysis against 100 mM acetate buffer, pH 5.5.To this mixture, a solution of trisuccin hydrazide. (43) (0.12 mol–1.2mol) in water (5 μl–20 μl) is added. The reaction mixture is stirred atroom temperature for 90 min at which time 20 μl of NaCNBH₃ solution inwater is added to a final concentration of 100 mM in NaCNBH₃. Theresulting mixture is stirred gently at room temperature for 18 hfollowed by purification of the conjugate by size-exclusion HPLC(SEC-HPLC) and eluted with DPBS.

For ^(99m)Tc-labelling, the procedure reported previously is used (42,43). Briefly, the ^(99m)Tc, eluted from a ⁹⁹Mo/^(99m)Tc generator(Syncor, Birmingham, Ala.) is reduced with a solution of SnCl₂ inhydroxyisobutyric acid at room temperature. This solution is added tothe trisuccin scFv and incubated at 35° C. for 30 min. The labelledprotein is purified by SEC-HPLC.

Alternately for direct ^(99m)Tc labelling, cysteine molecules on thepurified scFv is radiolabeled with ^(99m)Tc by previously publishedmethods using a ^(99m)Tc-D-glucarate transfer method (44, 45). Moleculartechniques is used to add a cysteine molecule near the COOH-terminal endof the scFv which will be available for this site directed labellingmethod. The radiolabelled protein is purified by SEC-HPLC.

Testing the Binding Ability of the Radiolabelled scFv

Whole cells or cell membranes from the three breast cancer cell lineswere used in a standard competitive radioimmunoassay to determine if theradiolabelled scFv retains its ability to bind to the EGFR. Theradiolabelled scFv used in competition with unlabelled scFv and assayswere counted in a gamma counter.

Human Breast Cancer Xenograft Models

Initially, 3 groups of 3 female athymic nude mice, 6 to 8 weeks old,obtained from the National Cancer Institute Frederick ResearchLaboratory (Frederick, Md.) are injected subcutaneously in the one flankwith 2×10⁷ human breast cancer cells. Each group is injected with one ofthe three breast cancer cell lines, MDA-MB-468, MDA-MB-231 and MCF-7.When the tumors are approximately 10 mm in diameter, the opposite flankare injected with the same cell line. When the second xenograft isapproximately 1 mm in diameter, the mice are injected with the^(99m)Tc-scFv and imaged. The xenograft model are repeated 2 additionaltimes and modified if necessary to produce consistent, reproducibleresults.

In Vivo Detection of Breast Cancer Tumors

Planar imaging of mice is performed using Picker Axis gamma cameraequipped with a pinhole collimator with 2-mm or 4-mm aperture. Theimages are acquired with a matrix of 256×256 pixels and a zoom factor of2. Studies are performed using a 20% energy window, centered on 140 keVphoto-peak of ^(99m)Tc. Mice are imaged immediately after beinganesthetized. Previous imaging studies suggest that most mice could beimaged for 45–60 minutes before they recover from the anesthesia. Eachmouse receives 50 μCi ^(99m)Tc-scFv IV. Mice are imaged in a proneposition as xenografts are planted subcutaneously in both ventralflanks. A distance of 7.5 cm from pinhole to mice is used for imaging agroup of 3 mice simultaneously in one field of view. Dynamic image isperformed at 0–1 h, 60 frames of images are acquired at 1 min/frame rateto obtain fast phase for scFv uptake in normal tissue and the tumor.Static images are acquired at 2 h, 4 h, 6 h, respectively. Acquisitiontime of each image is 20–30 min, which is comparable to that of patientimaging using a gamma camera.

These images are used to determine the optimal imaging time and besttumor to non-tumor image contrast that can be used for future patientimaging. This imaging computerized kinetic model allows one to obtainpharmacokinetics information in same animals and provide direct evidencefor the potential of using ^(99m)Tc-human anti-EGFR-scFv for earlydetection of breast cancer in patients.

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Any patents or publications mentioned in this specification areindicative of the levels of those skilled in the art to which theinvention pertains. These patents and publications are hereinincorporated by reference to the same extent as if each individualpublication was specifically and individually indicated to beincorporated by reference.

One skilled in the art will readily appreciate that the presentinvention is well adapted to carry out the objects and obtain the endsand advantages mentioned, as well as those inherent therein. The presentexamples along with the methods, procedures, treatments, molecules, andspecific compounds described herein are presently representative ofpreferred embodiments, are exemplary, and are not intended aslimitations on the scope of the invention. Changes therein and otheruses will occur to those skilled in the art which are encompassed withinthe spirit of the invention as defined by the scope of the claims.

1. An isolated human anti-epidermal growth factor receptor single-chainantibody comprising the amino acid sequence of SEQ ID No. 2 or abiologically functional fragment thereof wherein said antibody binds tothe enidermal arowth factor receptor.
 2. A composition comprising theanti-epidermal growth factor receptor single-chain antibody of claim 1and a pharmaceutically acceptable carrier.
 3. The pharmaceuticalcomposition of claim 2, further comprising a therapeutic agent.
 4. Thecomposition of claim 3, wherein said therapeutic agent is selected fromthe group consisting of a toxin, a chemotherapeutic agent, aradioisotope and gene therapy vector.
 5. The composition of claim 2,further comprising a diagnostic agent.
 6. The composition of claim 2,wherein said diagnostic agent is a radioisotope or a transition metal.7. The anti-epidermal growth factor receptor single-chain antibody ofclaim 1, wherein said antibody is radiolabeled.